Liquid resin composition for abrasive articles

ABSTRACT

The invention relates to a thermally curable liquid resin composition intended for manufacturing abrasives that comprises at least one epoxy resin comprising at least two epoxy groups and at least one reactive diluent, said composition having a viscosity, at 25° C., less than or equal to 7000 mPa.s. 
     Application of the resin composition for producing abrasive articles, especially bonded abrasives and coated abrasives. 
     It also relates to the abrasive articles comprising abrasive grains connected by such a liquid resin composition.

The present invention relates to a thermally curable liquid resincomposition capable of being used in the manufacture of abrasivearticles, and to the resulting abrasive articles.

Abrasive articles generally incorporate a multitude of abrasive grainsfirmly bound to a support or together by a binder. These articles arewidely used for machining various materials, especially in cutting,grinding, deburring and polishing operations.

Conventionally, a distinction is made between coated abrasives andbonded abrasives.

Coated abrasives comprise a generally flexible support material, spreadon the surface of which are abrasive grains set in a binder. Theflexible support may be a sheet of paper, a film or a network of fibres,for example a mat, a felt, a woven or a knit of natural or syntheticfibres, especially made from glass or a polymer. These abrasives mayadopt various forms: sheets, strips, discs, etc.

The manufacture of coated abrasives comprises the application of a makecoat on the support material, the distribution of the abrasive grains onsaid coat, heat-treatment of the make coat with a view to partiallycuring it and the application of a size coat which guarantees a firmanchoring of the grains on the support. A supersize coat may bedeposited on the size coat and the abrasive grains.

The make, size and supersize coats are applied in liquid form. They aregenerally composed of a thermosetting resin, especially a resol typephenolic resin.

Bonded abrasives are composed of abrasive grains bound together by abinder which makes it possible to have a three-dimensional structuresuitable for carrying out abrasion operations, especially cutting hardmaterial such as steel. Generally, these abrasives have the appearanceof a grinding wheel, a grinding wheel segment and a whetstone.

Bonded abrasives in the form of “conventional” grinding wheels areformed from a single region composed of abrasive grains embedded in thebinder which extends from the bore to the periphery of the wheel. In“superabrasive” wheels the abrasion region is located at the periphery,in the form of a strip supported by a central core generally made ofmetal, and the abrasive grains are composed of a very hard material, forexample diamond or cubic boron nitride.

Bonded abrasives are obtained by the process using cold or hotcompression moulding techniques.

In cold compression moulding, which is the most widespread, the mixtureof the abrasive constituents, in granular form, is introduced into amould, then a sufficient compressive force is applied, of around 15 to25 N/mm², to make said mixture into the shape of the mould and to ensurethat, after extraction from the mould, the part obtained (green article)has sufficient strength in order to be able to be handled without losingits initial shape. The part is then heated in an oven at a temperaturethat allows the binder to be crosslinked, this temperature depending onthe nature of the binder used.

Hot compression moulding makes it possible to achieve a higher level ofcompaction than cold moulding, which is expressed by a lower pore volumein the final article. In this process, the granular mixture introducedinto the mould is compacted under pressure and simultaneously heated inorder to enable the binder to spread out better between the abrasivegrains and to occupy the empty spaces. After having been removed fromthe mould, the part generally undergoes a post-crosslinking heattreatment that aims to improve its operating lifetime and its abrasionperformance.

Whatever type of compression moulding used, either cold or hot, it isessential that the mixture of the abrasive constituents is in granularform.

The preparation of the granular mixture is carried out by pretreatingthe abrasive grains with a liquid impregnation resin, in general a resoltype phenolic resin, then by mixing the wet grains with a novolac typephenolic resin powder containing a crosslinking agent—powder which willsubsequently form the binder itself—and if necessary additives, also inpowder form. The mixture obtained is thus composed of abrasive grains,bonded to the surface of which are solid resin and additive particles.This mixture has a good ability to be uniformly distributed in the mould(referred to as “flowability”) and to be shaped under the effect ofpressure.

The resol type thermosetting resins used for manufacturing coated andbonded abrasives have many advantages under the intended usageconditions, especially:

-   -   they provide a solid bond between the grains and the support        material, on the one hand, and between the grains themselves, on        the other hand;    -   they withstand well the high mechanical stresses that occur        under the peripheral high-speed grinding conditions, which makes        it possible to prevent the tool from breaking; and    -   their high thermal resistance makes it possible to limit the        risk of excessive heat build-up within the tool.

One drawback of the aforementioned resols lies in the fact that theycontain formaldehyde which is harmful to human health and to theenvironment.

It is known that resols contain free formaldehyde which may be emittedinto the atmosphere during the manufacture of the abrasives, and thatthey can, in addition, generate formaldehyde under the usage conditionsof the abrasive, when the temperature reaches a level that leads to thedegradation of the resol with release of formaldehyde.

For several years now, the regulations regarding formaldehyde emissionshave been getting stricter and tend to limit the amount of formaldehydewhich is contained in abrasives or which may be emitted from theseproducts.

Many resin compositions having a low formaldehyde content have beenproposed.

Proposed in U.S. Pat. No. 6,133,403 are reactive diluents for phenoliccompositions and crosslinkable novolacs intended for producing compositematerials that have a high impact strength.

WO 2005/108454 A1 describes a novolac resin and non-formaldehydehardener composition for reinforcing composites.

Described in U.S. Pat. No. 5,523,152 is a curable composition forabrasives that comprises an aminoplast resin and a reactive diluentwhich both contain unsaturated pendant groups.

U.S. Pat. No. 5,178,646 describes a binder precursor composition forabrasives, especially coated abrasives, which comprises a thermallycurable resin having a plurality of pendant methylol groups and areactive diluent having at least one functional group that reacts withthe groups of the resin.

U.S. Pat. No. 5,549,719 describes a composition intended to form thebase adhesive layer of coated abrasives. The composition comprises anaqueous dispersion of an epoxy resin, an emulsifier and a crosslinkingagent, and if necessary an agent that aids the abrasion. This aqueouscomposition makes it possible to replace the compositions based onorganic solvents whose use becomes more restrictive but in return makesit necessary to treat the abrasives in a steam plant in order to removethe water.

The present invention aims to reduce the amount of formaldehyde andwater in an abrasive product.

For this purpose, the invention provides a thermally curable liquidresin composition which forms an alternative to the resols and to theaqueous epoxy resins used as an adhesive in coated abrasives and as animpregnation resin in bonded abrasives, this liquid resin compositionbeing characterized in that it comprises at least one resin comprisingat least two epoxy groups and at least one reactive diluent, and in thatit has a viscosity, at 25° C., less than or equal to 7000 mPa.s.

Preferably, the liquid resin composition has a viscosity of less than orequal to 6000 mPa.s, measured at 25° C.

The epoxy resin may be chosen from any type of resin comprising at leasttwo, preferably at most 10, epoxy functional groups. The expression“epoxy functional group” is understood to mean a group containing anoxirane ring.

Generally, the epoxy resin has an epoxide equivalent weight that variesfrom 160 to 700, preferably less than or equal to 500 and advantageouslyless than or equal to 350. The epoxide equivalent weight (EEW) is theratio of the average molecular weight of the resin to the average numberof epoxy functional groups per molecule.

According to a first embodiment of the invention, the epoxy resin ischosen from the epoxy resins of which the main chain is aliphatic,cycloaliphatic or aromatic. Preferably, the epoxy resin is an aromaticepoxy resin, advantageously of the bisphenol A or F type, in particularthe bisphenol A or F diglycidyl ether of formula:

with: n=0-10, preferably 1-4, and R═H or CH₃, preferably CH₃.

The epoxy resins of bisphenol A or F type may be obtained by reacting abisphenol A or F with an excess of epichlorohydrin, in the presence of abasic catalyst, for example sodium hydroxide, at a temperature of around100° C.

According to a second embodiment, the epoxy resin is chosen fromepoxidized novolac resins.

The epoxidized novolac resin may be obtained by treating a novolac resinwith an excess of epichlorohydrin in the presence of a basic catalyst,for example sodium hydroxide, at a temperature of around 100° C.

The novolac resin may be chosen from the novolacs known to a personskilled in the art which are obtained by reaction of a phenolic compoundand an aldehyde in an aldehyde/phenolic compound molar ratio of lessthan 1, in the presence of an acid catalyst.

The phenolic compound is chosen from phenol and substituted phenols suchas cresols, guaiacol, methoxyphenols, catechol, resorcinol,tert-butylphenol and nonylphenol, bisphenols such as bisphenol A or F,naphthols and mixtures of these compounds. Preferably, phenol is chosen.

The aldehyde is chosen from alicyclic aldehydes such as formaldehyde,cyclic aldehydes such as furfural, aromatic aldehydes such asbenzaldehyde, para-anisaldehyde, ortho-anisaldehyde and veratraldehyde,and mixtures of these aldehydes. Preferably, formaldehyde is chosen.

Preferably, the aldehyde/phenol molar ratio varies from 0.2 to less than1, advantageously from 0.35 to 0.9 and better still from 0.5 to 0.9.

The novolac resin may be prepared by using a known acid catalyst, forexample a strong mineral acid such as sulphuric acid, phosphoric acidand hydrochloric acid, or an organic acid such as oxalic acid, salicylicacid or anhydrides such as maleic anhydride. The amount of acid must besufficient to allow the condensation of the phenolic compound and of thealdehyde. The amount of acid used generally represents from 0.02 to 1%of the weight of the starting phenolic compound, preferably 0.1 to 0.6%in the case of a strong mineral acid, and from 0.3 to 3% of the weightof the starting phenolic compound in the case of an organic acid.

Preferably, the novolac resin obtained at the end of the condensationreaction is treated so as to reduce the content of free phenoliccompound, for example by vacuum distillation.

The preferred epoxidized novolacs correspond to the formula:

with R′═H or

in which R═H or CH₃, preferably CH₃, and n′=0-4, preferably 0.1-2.

The novolacs that can be used within the scope of the invention containless than 0.1% by weight of free formaldehyde, and preferably less than0.05%. They advantageously have a low molecular weight, less than 3000g/mol.

The epoxy resin may be composed of a mixture of at least one epoxidizedaromatic resin and at least one epoxidized novolac resin describedabove.

The resin composition may also comprise at least one resin differentfrom the epoxy resin according to the invention capable of reacting withsaid epoxy resin and/or the crosslinking agent as explained later on forexample a novolac. The proportion of epoxy resin must however remaingreater than or equal to 50% by weight of all the resins, epoxy resin(s)and other resin(s), preferably greater than or equal to 75% andadvantageously the proportion is equal to 100%.

The epoxy resin represents at least 30% by weight of the resincomposition, preferably at least 40% and advantageously at least 50%,and does not exceed 90%.

The reactive diluent according to the invention is a compound which isliquid at room temperature, around 20 to 25° C., which makes it possibleto dissolve the epoxy resin and to adjust the viscosity of the resincomposition.

Preferably, the reactive diluent has a viscosity, measured at 25° C.,less than or equal to 1000 mPa.s, preferably less than or equal to 700mPa.s, advantageously less than 500 mPa.s and better still less than 350mPa.s.

The reactive diluent also contains at least one functional group capableof reacting with the resin and/or the crosslinking agent, a functionalgroup that is chosen from the hydroxy, aldehyde, epoxy, oxazolidine andlactone functional groups.

As examples of reactive diluents comprising hydroxy functional groups,mention may be made of saturated or unsaturated alicyclic alcohols, suchas ethylene glycol, 1,3-butylene glycol, glycerol, trimethylolpropaneand the monoallyl ethers of these compounds, saturated or unsaturatedcyclic alcohols, such as furfuryl alcohol, mononuclear or polynucleararomatic alcohols, such as benzyl alcohol and its derivatives, m-cresol,3,5-xylenol, nonylphenol, cardanols and their derivatives such ascardols, methyl cardols and anacardic acids especially contained incashew nut shells (“cashew nut shell liquid”) denoted as CNSL), andnaphthol, and the precursors of these alcohols, especially acetals andtrioxanes.

As examples of reactive diluents comprising aldehyde functional groups,mention may be made of glyoxal.

As examples of reactive diluents comprising epoxy functional groups,mention may be made of glycidyl ethers of saturated or unsaturatedalcohols such as 1,4-butanediol diglycidyl ether, 1,6-hexanedioldiglycidyl ether, epoxidized fatty acids especially contained inepoxidized oils, in particular soybean oil (ECOCET®, from Arkema) andlinseed oil (VIKOFLEX®, from Arkema), aromatic epoxies such asepoxidized cardanols, especially 3-n-pentadecadienylphenol.

As examples of reactive diluents comprising oxazolidine functionalgroups, mention may be made of3-ethyl-2-methyl(3-methylbutyl)-1,3-oxazolidine,1-aza-3,7-dioxa(5-ethyl)bicyclo[3.3.0]octane and bisoxazolidines.

The preferred reactive diluent comprising a lactone functional group isgamma-butyrolactone. Advantageously, gamma-butyrolactone is used inadmixture with triphenylphosphite, which permits to improve the thermalbehaviour of the liquid resin composition.

The preferred diluents are furfuryl alcohol, cardols and derivativesthereof (CNSL), glyoxal, 1,4-butanediol diglycidyl ether, 1,6-hexanedioldiglycidyl ether, epoxidized cardanols, bisoaxazolidines andgamma-butyrolactone.

The reactive diluent represents at least 10% by weight of the resincomposition, preferably at least 20%, and advantageously does not exceed70%, preferably 30%. Below 10%, the viscosity of the resin compositionis too high for it to be used in the targeted applications. Above 70%,the mechanical properties of the final abrasive product are notsatisfactory.

The resin composition may comprise, in addition, at least onecrosslinking agent and/or at least one crosslinking catalyst.

The crosslinking agent must have a high reactivity with regards to theepoxy resin and/or the reactive diluent.

The crosslinking agent is chosen from compounds incorporating at leastone amine, hydroxy, aldehyde or carboxylic functional group, andheterocyclic compounds that have a structure incorporating a nitrogenatom and an oxygen atom separated by a carbon atom.

As examples of compounds incorporating at least one amine functionalgroup, mention may be made of aliphatic amines such astriethylenetetramine (TETA) and triethylenepentamine (TEPA),polyamidoamines and aromatic polyamines such as diaminodiphenylmethane(MDA) and diaminodiphenyl sulphone (DDS).

As examples of compounds that incorporate at least one hydroxyfunctional group, mention may be made of tris(hydroxymethyl)nitromethaneand resins comprising condensates obtained by Mannich reaction of aphenolic compound, an aldehyde and an amino alcohol as especiallydescribed in WO 2004/011519 A1, in particularphenol-formaldehyde-diethanolamine resins.

As examples of compounds incorporating at least one aldehyde functionalgroup, mention may be made of glyoxal and its derivatives, and2,2-dimethoxyethanal.

As examples of compounds incorporating at least one carboxylicfunctional group, mention may be made of acrylic acid homopolymers andcopolymers.

As examples of heterocyclic compounds incorporating a nitrogen atom andan oxygen atom separated by a carbon atom, mention may be made ofoxazolines such as 1,3-phenylenebisoxazoline and oxazolidines such as3-ethyl-2-methyl-2-(3-methylbutyl)-1,3-oxazolidine and1-aza-3,7-dioxa(5-ethyl)bicyclo[3.3.0]octane.

The preferred crosslinking agent is tris(hydroxymethyl)nitromethane,glyoxal and its derivatives, 2,2-dimethoxyethanal, resins containingcondensates obtained by Mannich reaction of a phenolic compound, analdehyde and an amino alcohol, acrylic acid homopolymers,1,3-phenylenebisoxazoline,3-ethyl-2-methyl-2-(3-methylbutyl)-1,3-oxazolidine and1-aza-3,7-dioxa(5-ethyl)bicyclo(3.3.0]octane.

The crosslinking agent does not exceed 50% of the weight of the liquidresin composition and preferably does not exceed 30%.

The liquid resin composition may also comprise at least one crosslinkingcatalyst chosen from Lewis bases such as O-(dimethylaminoethyl)phenol,tris(dimethyl-aminoethyl)phenol, 2,4,6-tri(dimethylaminomethyl)-phenol,2-methylimidazole, 2-ethyl-4-methylimidazole and1-benzyl-2-methylimidazole, and Lewis acids such as the borontrifluoride-monoethyleneamine complex.

The preferred catalyst is 2,4,6-tri(dimethylaminomethyl)-phenol,2-methylimidazole and 2-ethyl-4-methylimidazole.

The amount of catalyst in the liquid resin composition is less than orequal to 10 parts by weight per 100 parts by weight of epoxy resin,reactive diluent and, if necessary, crosslinking agent, and preferablyis less than or equal to 5 parts.

Preparation of the liquid resin composition may be carried out by simplemixing of the constituents in a suitable vessel, advantageously equippedwith stirring means; preferably, the novolac resin is introduced intothe reactive diluent, then, if necessary, the crosslinking agent and/orthe catalyst are added.

The constituents may be mixed at room temperature, around 20 to 25° C.,or at a higher temperature, but which must remain at least 20° C. belowthe crosslinking temperature of the resin composition.

The viscosity of the liquid resin composition depends on the targetedapplication but remains less than or equal to 7000 mPa.s.

According to a first variant embodiment of the invention, the liquidresin composition according to the invention is used to manufacturebonded abrasives.

The liquid resin composition is first mixed with abrasive grains in aconventional mechanical mixer until the grains are suitably “wetted”,that is to say are coated with the resin composition, then the powderedbinder and the additives, also powdered, are added until a homogeneousgranular mixture is obtained.

Preferably, the liquid resin composition has a viscosity at most equalto 3000 mPa.s, and advantageously greater than or equal to 600 mPa.s, at25° C.

The crosslinking start temperature of the resin in the granular mixtureis at most equal to 245° C., and advantageously at most equal to 195° C.

The time required to obtain complete crosslinking of the resincomposition in the granular mixture is less than or equal to 36 hours,preferably less than or equal to 20 hours.

The abrasive grains may be any type of known abrasive grains, forexample made of alumina, including therein fused aluminas and sinteredaluminas obtained by the sol-gel process, which may or may not be seededby a material of the same crystalline nature, and which may or may notbe chemically modified, of iron oxide, molybdenum oxide, vanadium oxide,alumina-zirconia, boron-alumina, silicon carbide, aluminium oxynitride,diamond or cubic boron nitride, and mixtures of such grains. Preferably,the abrasive grains are made of alumina.

Preferably, the abrasive grains are pretreated with an organic compoundthat improves the adhesion between the grain and the liquid resincomposition, chosen from compounds that contain silicon, for example asilane functionalized by organic groups such as a vinylsilane,especially vinyltriethoxysilane, an aminosilane, especiallyγ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane anddiaminopropyl- and or an epoxysilane. Preferably,γ-aminopropyltriethoxysilane is used.

The abrasive grains may be treated with the organic compound thatcontains silicon by, for example, spraying a solution of said compoundin a suitable solvent or by dispersing the grains in the aforementionedsolution. The treated abrasive grains are dried before being mixed withthe liquid resin composition.

If necessary, it is possible to add to the abrasive grain and resincomposition mixture; an organic liquid medium which helps to wet thegrains and to form a uniform grain network, and which is subsequentlyremoved during the crosslinking step. The organic medium may be water,an aliphatic alcohol, a glycol, high molecular weight petroleumfractions of oily or waxy consistency, a mineral oil or any other knownmedium.

The binder may be a phenol-aldehyde, melamine-aldehyde, urea-aldehyde,polyester, polyimide, epoxy, polyurethane or polybenzimidazole resin.Preferably, the binder is a resin having a low level of formaldehyde,advantageously a phenol-aldehyde resin of novolac type, and better stilla phenol-formaldehyde novolac resin.

The additives are, for example, fillers, crosslinking agents and othercompounds used for manufacturing bonded abrasives, especially thosebonded by an organic resin.

The fillers are generally in the form of a finely divided powdercomprising particles which may have the appearance, in particular, ofgranules, spheres or fibres. As examples, mention may be made of sand,silicon carbide, hollow alumina spheres, bauxite, chromites, magnesite,dolomites, hollow mullite spheres, borides, fumed silica, titaniumdioxide, carbon-based products (carbon black, coke, graphite, etc.),wood flour, clay, talc, hexagonal boron nitride, molybdenum disulphide,feldspar, nepheline syenite and glass, in particular in the form ofsolid, cellular or hollow beads, and fibres. Generally, fillersrepresent 0.1 to 30% by weight of the granular mixture.

Crosslinking agents are used when the powdered binder is a novolacresin. They may be chosen from the compounds known for providing theaforementioned function such as hexamethylenetetramine or precursorsthereof. The crosslinking agent is added in an amount of 5 to 20 partsby weight per 100 parts by weight of powdered novolac resin.

The additives may also comprise agents which help in carrying out theprocess, for example antistatic agents and lubricants. The amount ofthese additives may be easily determined by a person skilled in the art.

Preferably, the granular mixture is subjected to a curing treatment atambient temperature for a duration of around 12 hours.

The granular mixture is then introduced into a mould equipped withcompression means that makes it possible to form a green article thathas sufficient cohesion to be able to be handled and treated in thefollowing steps without a substantial change in its shape. At this stagethe binder is in the non-crosslinked state.

The green article is then heated at a sufficient temperature so that thebinder may crosslink and give a rigid polymer network that imparts tothe article its final shape. Crosslinking is carried out according to aconventional curing cycle that consists in bringing the green article toa temperature of around 100° C. and in keeping it at this temperaturefor 30 minutes to several hours so that the volatile products formed canbe discharged. Next, the article is heated at the final temperature fora duration that generally varies from 10 to 36 hours.

The final crosslinking temperature especially depends on the nature ofthe resin used, on the size and shape of the part to be treated and alsoon the curing duration. In general, the final crosslinking temperatureis between 100 and 200° C.

Thermal crosslinking is carried out in a controlled atmosphere,preferably) with a maximum degree of relative humidity.

The bonded abrasives obtained may be in the form of grinding wheels,grinding wheel segments, discs and whetstones.

According to a second variant embodiment of the invention, the liquidresin composition according to the invention is used to manufacturecoated abrasives.

As already indicated, the manufacture of coated abrasives comprises thesteps that consist in depositing a make coat on a support material, inspreading the abrasive grains on said coat, subjecting said material toa heat treatment that makes it possible to partially crosslink the resincomposition, depositing a size coat and subjecting the coated materialto a heat treatment so as to obtain the complete crosslinking of theresin composition. If necessary, a supersize coat may be deposited onthe size coat and crosslinked by a suitable heat treatment.

The support material generally has a moderate to high flexibility, andhas the appearance of a sheet, especially of paper, a film, especially apolymer film, or a more or less dense network of natural or syntheticfibres, for example glass fibres and vulcanized fibres.

The abrasive grains may be chosen from the grains already mentioned thatare incorporated into the composition of bonded abrasives.

The application of the grains onto the make coat may be carried out bythe usual techniques that operate by gravity or by an electrostaticroute. The density of the abrasive grains on the support is chosen as afunction of the desired application.

The liquid resin composition according to the invention may be used toform the make coat, the size coat or the supersize coat. Preferably, theliquid resin composition is used to form the make coat and the sizecoat, and where necessary the supersize coat.

Preferably, the liquid resin composition has a viscosity less than orequal to 6000 mPa.s and a crosslinking start temperature at most equalto 150° C., advantageously at most equal to 120° C. It advantageouslycontains at least one crosslinking agent or at least one crosslinkingcatalyst.

The time required to obtain complete crosslinking of the resincomposition is less than 36 hours, preferably less than 20 hours.

The make, size and supersize coats which are not formed from the liquidresin composition according to the invention may be chosen fromphenolic, urea-formaldehyde, epoxy, urethane, acrylic, aminoplast andmelamine resins, and mixtures of these resins. Preferably, the resin orresin mixture has the lowest possible level of free formaldehyde.

The liquid resin composition may comprise, in addition, additives, forexample wetting agents, fillers, coupling agents, dyes, pigments andantistatic agents.

When the liquid resin composition is used to form the size coat and/orthe supersize coat, it advantageously comprises at least one agent thatstrengthens the abrasive performance of the final abrasive. Such anagent may be chosen from waxes, organic halogenated compounds, halogensalts, metals and metal alloys.

The heat treatment of the support material coated with the liquid resincomposition forming the make coat is carried out at a temperature lessthan or equal to 150° C., preferably less than or equal to 120° C. for 1to 120 minutes, preferably 1 to 60 minutes.

The heat treatment conditions for crosslinking the resin compositionforming the size coat or supersize coat may be carried out at atemperature less than or equal to 150° C., preferably less than or equalto 120° C. for at most 36 hours, preferably at most 20 hours.

The examples given below make it possible to illustrate the inventionwithout however limiting it.

In the examples, the properties of the liquid resin compositions aremeasured under the following conditions:

-   -   the crosslinking start temperature is measured by dynamic        mechanical analysis (DMA): the liquid resin composition is        introduced between two glass plates and the assembly is        positioned horizontally in a device comprising two lower jaws        fixed at a distance of 40 mm apart and an upper jaw applied        against the upper sheet located at 20 mm from each of the        preceding jaws. A force of 80 mPa is applied to the upper jaw        with an oscillation frequency of 1 Hz, while heating the        assembly from 25 to 300° C. at the rate of 4° C./minute. The        elastic modulus of the resin composition is measured as a        function of the temperature and the crosslinking start        temperature is determined from the established curve.    -   the weight loss at 400° C. is determined by thermogravimetric        analysis (TGA): the liquid resin composition is deposited in an        aluminium pan and heated according to a given temperature cycle.        10 to 20 mg of the crosslinked resin composition are placed in        an alumina crucible which is put into a machine continuously        measuring the weight loss during a temperature cycle ranging        from 25 to 700° C. at the rate of 10° C./minute. The weight loss        at 400° C. is determined from the recorded curve.

EXAMPLES 1 TO 24

a) Liquid resin compositions having the composition given in Table 1 (inparts by weight) were prepared.

The resins were obtained by dissolving the epoxy resin in the reactivediluent, with moderate stirring, then by adding, if necessary, thecrosslinking agent and/or the catalyst while maintaining the stirringconditions.

The resin was dissolved at ambient temperature, around 20 to 25° C. forthe BADGE (epoxidized bisphenol A type resin) and at a temperature ofaround 50° C. for the epoxidized novolac resin.

The liquid resin compositions (Examples 1 to 24), and also the referencecompositions (Ref. 1 to 3) were treated according to the followingtemperature cycles:

-   -   Cycle No. 1 (coated abrasives)        -   hold at 70° C. for 35 minutes;        -   70 to 80° C. in 5 minutes;        -   hold at 80° C. for 50 minutes;        -   80 to 90° C. in 5 minutes;        -   hold at 90° C. for 50 minutes;        -   90 to 100° C. in 5 minutes;        -   hold at 100° C. for 42 minutes;        -   100 to 115° C. in 5 minutes; and        -   hold at 115° C. for 42 minutes.    -   Cycle No. 2 (bonded abrasives)        -   cycle No. 1; and        -   200° C. for 2 hours.

The reference compositions 1 and 2 (Ref. 1 and 2) were liquidcompositions suitable for producing coated abrasives based on aphenol-formaldehyde resol and a urea-formaldehyde resin/respectively.The reference composition 3 (Ref. 3) was a liquid composition based on aphenol-formaldehyde resol which was suitable for manufacturing bondedabrasives.

The crosslinking start temperature and the weight loss at 400° C. forthe resin compositions are given in Table 1.

b) The liquid resin compositions of Examples 8 and 22, and of thereference 3 were used to form mixtures with a solid novolac resin⁽¹²⁾suitable for manufacturing bonded abrasives. The mixtures comprised (inweight %): 12.7% of the liquid resin composition and 87.3% of the solidresin.

The weight loss at 400 and 500° C. was determined for the mixturestreated under the thermal conditions of cycle No. 2.

Weight loss (%) Liquid resin composition 400° C. 500° C. Ex. 8 3.8 39.7Ex. 22 4.9 32.2 Ref. 3 5.4 39.7

EXAMPLES 25 TO 39

Liquid resin compositions having the composition (in parts by weight)given in Table 2 were prepared in the conditions of examples 1 to 24.

The resins were obtained by dissolving the epoxy resin in the reactivediluent, with moderate stirring, then adding, if necessary, the catalystwhile maintaining the stirring conditions.

The resin was dissolved at a temperature of around 35 to 50° C.

The liquid resin compositions are treated according to the temperaturecycles 1 and 2 disclosed in examples 1 to 24.

The crosslinking start temperature and the weight loss at 400° C. forthe resin compositions are given in Table 2.

-   -   (1) Sold under the reference EPIKOTE® 828 by Hexion Specialty        Chemicals; bisphenol A diglycidyl ether (BADGE) resin; EEW:        184-190.    -   (2) Sold under the reference EPIKOTE® 600 by Hexion Specialty        Chemicals; epoxidized phenol-novolac resin; EEW: 180-200.    -   (3) Sold under the reference HELOXY® MODIFIER BD by

Hexion.

-   -   (4) Sold under the reference NC513 by Cardolite Europe.    -   (5) Sold under the reference Cashew Nut Shell Liquid (CNSL) by        Palmer Ltd.; Cardanol content (>60 wt %).    -   (6) Sold under the reference HELOXY® MODIFIER HD by Hexion.    -   (7) Sold under the reference ZOLDINE® MS PLUS by Angus Dow.    -   (8) Sold under the reference INCOZOL® LV by Incorez.    -   (9) Sold under the reference ACUSOL® 445 by Rohm & Haas; average        molecular weight: 4500.    -   (10) Resin based on phenol-formaldehyde-amino alcohol        condensates according to Example 2(a) of WO 2004/011519 A1,        modified in that the amino alcohol is diethanolamine.    -   (11) Sold under the reference HIGHLINK® CDO by Clariant; 60V        solution in water.    -   (12) Sold under the reference BAKELITE® 8686 by Hexion Specialty        Chemicals; contains 7 wt % of hexamethylenetetramine (HEXA).    -   (13) Sold under the reference BAKELITE® PF8505F by Hexion        Specialty Chemicals.

TABLE 1 Crosslinking Weight loss Weight loss R/RD/CA/C start at 400° C.at 400° Reactive diluent Crosslinking Catalyst (parts by temperatureafter cycle after cycle Ex. Resin (R) (RD) agent (CA) (C) weight) (° C.)1 (%) 2 (%)  1 BADGE⁽¹⁾ furfuryl alcohol — 2MI 90/10/0/2 84 9.4 n.d.  2BADGE⁽¹⁾ 1,4-butanediol — 2MI 90/10/0/2 90 n.d. 20.4 diglycidyl ether⁽³⁾ 3 BADGE⁽¹⁾ 1,6-hexanediol — 2MI 90/10/0/2 99 n.d. 31.3 diglycidylether⁽⁶⁾  4 BADGE⁽¹⁾ epoxidized — 2MI 90/10/0/2 93 n.d. 12.9cardanols⁽⁴⁾  5 BADGE⁽¹⁾ CNSL⁽⁵⁾ — 2MI 90/10/0/2 93 12.7 n.d.  6BADGE⁽¹⁾ glyoxal — 2MI 90/10/0/2 132 49.9 n.d.  7 BADGE⁽¹⁾bisoxazolidine⁽⁸⁾ — 2MI 90/10/0/2 n.d. n.d. 18.8  8 epoxidized Furfurylalcohol — 2MI 70/30/0/2 n.d. 16.0 n.d. novolac⁽²⁾  9 epoxidized Furfurylalcohol 3-ethyl-2- — 50/20/30/0 250 n.d. 33.4 novolac⁽²⁾ methyl(3-methylbutyl)- 1,3- oxazolidine⁽⁷⁾ 10 epoxidized Furfuryl alcohol 1,3-PBO— 50/20/30/0 183 n.d. 19.3 novolac⁽²⁾ 11 epoxidized furfuryl alcohol TNE— 50/20/30/0 195 n.d. 20.0 novolac⁽²⁾ 12 epoxidized furfuryl alcohol1-aza-3,7- — 50/20/30/0 226 n.d. 16.5 novolac⁽²⁾ dioxa(5- ethyl)bicyclo[3.3.0]octane 13 epoxidized furfuryl alcohol glyoxal — 50/20/30/0 136n.d. 31.3 novolac⁽²⁾ 14 epoxidized furfuryl alcohol acrylic — 50/20/30/0244 n.d. n.d. novolac⁽²⁾ polymer⁽⁹⁾ 15 epoxidized furfuryl alcoholP-F-DEA — 50/20/30/0 133 n.d. 21.7 novolac⁽²⁾ resin⁽¹⁰⁾ 16 epoxidizedfurfuryl alcohol 2,2-dimethoxy- — 50/20/30/0 214 n.d. 20.6 novolac⁽²⁾ethanal 17 epoxidized furfuryl alcohol acrylic 2MI 50/20/30/2 144 n.d.n.d. novolac⁽²⁾ polymer⁽⁹⁾ 18 epoxidized furfuryl alcohol glyoxal —50/20/30/0 n.d. n.d. 49.5 novolac⁽²⁾ derivative⁽¹¹⁾ 19 epoxidized1,6-hexanediol — 2MI 70/30/0/2 155 n.d. 26.1 novolac⁽²⁾ diglycidylether⁽⁶⁾ 20 epoxidized 1,4-butanediol — 2MI 70/30/0/2 195 n.d. 30.3novolac⁽²⁾ diglycidyl ether⁽³⁾ 21 epoxidized epoxidized — 2MI 70/30/0/2225 n.d. 19.5 novolac⁽²⁾ cardanols⁽⁴⁾ 22 epoxidized CNSL⁽⁵⁾ — 2MI70/30/0/2 129 5.6 n.d. novolac⁽²⁾ 23 epoxidized glyoxal — 2MI 70/30/0/2n.d. 36.8 n.d. novolac⁽²⁾ 24 epoxidized bisoxazolidine⁽⁸⁾ — 2MI70/30/0/2 n.d. n.d. 15.8 novolac⁽²⁾ Ref. 1 PF resol — — — 100/0/0/0 12514.1 11.3 Ref. 2 UF resin — — — 100/0/0/0 119 74.3 n.d. Ref. 3 PF resol— — — 100/0/0/0 133 n.d.  8.9 n.d.: not determined; 2MI:2-methylimidazole; 1,3-PBO: 1,3-phenylenebisoxazoline TNE:tris(hydroxymethyl)nitromethane; P-F-DEA resin:phenol-formaldehyde-diethanolamine resin PF resol: phenol-formaldehyderesol; UF resin: urea-formaldehyde resin

TABLE 2 Cross- Resin/reactive linking start Weight loss at Weight lossResin diluent/catalyst temperature 400° C. after at 400° after Ex.(parts by weight) Reactive diluent Catalyst (parts by weight) (° C.)cycle 1 (%) cycle 2 (%) 25 epoxidized novolac⁽²⁾ γ-butyrolactone2,4,6-tri-(dimethylaminomethyl)- 70/30/2 106 n.d. n.d. phenol 26epoxidized novolac⁽²⁾/ γ-butyrolactone 2,4,6-tri-(dimethylaminomethyl)-70/30/2 110 30 8 novolac⁽¹³⁾ phenol 35/35 27 epoxidized novolac⁽²⁾/γ-butyrolactone/ 2,4,6-tri-(dimethylaminomethyl)- 70/30/2 n.d. 32 17novolac⁽¹³⁾ triphenylphosphite phenol 35/35 30/70 28 epoxidizednovolac⁽²⁾/ γ-butyrolactone/ — 70/30/2 n.d. 26 16 novolac⁽¹³⁾triphenylphosphite 35/35 30/70 29 epoxidized novolac⁽²⁾/γ-butyrolactone/ 2,4,6-tri-(dimethylaminomethyl)- 70/30/2 n.d. 34 29novolac⁽¹³⁾ triphenylphosphite phenol 35/35 70/30 30 epoxidizednovolac⁽²⁾/ γ-butyrolactone/ 2MI 70/30/2 112 37 24 novolac⁽¹³⁾triphenylphosphite 35/35 70/30 31 epoxidized novolac⁽²⁾/ furfurylalcohol 2MI 70/30/2 116 21 n.d. novolac⁽¹³⁾ 35/35 32 epoxidizednovolac⁽²⁾/ furfuryl alcohol/ 2,4,6-tri-(dimethylaminomethyl)- 70/30/2115 24 6 novolac⁽¹³⁾ γ-butyrolactone phenol 35/35 70/30 33 BADGE⁽¹⁾γ-butyrolactone 2MI 90/10/2 102 12 9 34 BADGE⁽¹⁾ γ-butyrolactone2-ethyl-4- 90/10/2 115  8 7 methylimidazole 35 BADGE⁽¹⁾/novolac⁽¹³⁾γ-butyrolactone 2MI 90/10/2 111 20 9 70/20 36 BADGE⁽¹⁾/novolac⁽¹³⁾γ-butyrolactone 2MI 80/20/2 115 20 13 50/30 37 BADGE⁽¹⁾/novolac⁽¹³⁾γ-butyrolactone/ 2,4,6-tri-(dimethylaminomethyl)- 70/30/2 n.d. 46 3935/35 triphenylphosphite phenol 30/70 38 BADGE⁽¹⁾/novolac⁽¹³⁾ furfurylalcohol 2MI 80/20/2 116 20 8 50/30 39 BADGE⁽¹⁾/novolac⁽¹³⁾ furfurylalcohol 2MI 90/10/2 107 20 11 70/20 n.d.: not determined; 2MI:2-methylimidazole

1. A thermally curable liquid resin composition intended formanufacturing abrasives, comprising at least one resin comprising atleast two epoxy groups and at least one reactive diluent, wherein saidcomposition has a viscosity, at 25° C., less than or equal to 7000mPa.s.
 2. The composition according to claim 1, wherein the resin has aviscosity less than or equal to 6000 mPa.s.
 3. The composition accordingto claim 1, wherein the epoxy resin has an epoxide equivalent weightthat varies from 160 to
 700. 4. The composition according to claim 1,wherein the epoxy resin is chosen from the epoxy resins of which themain chain is aliphatic, cycloaliphatic or aromatic.
 5. The compositionaccording to claim 4, wherein the resin is an aromatic resin.
 6. Thecomposition according to claim 5, wherein the resin is a bisphenol A orF diglycidyl ether of formula:

in which n=0-10, and R═H or CH₃.
 7. The composition according to claim1, wherein the epoxy resin is chosen from epoxidized novolac resins. 8.The composition according to claim 7, wherein the novolac is obtained bythe reaction of a phenolic compound and an aldehyde in analdehyde/phenol molar ratio which varies from 0.2 to less than
 1. 9. Thecomposition according to claim 7, wherein the epoxy resin corresponds tothe formula:

with R′═H or

in which R═H or CH₃, and n′=0.
 10. The composition according to claim 1,wherein the epoxy resin represents at least 30% by weight of the resincomposition, and does not exceed 90%.
 11. The composition according toclaim 1, wherein the reactive diluent has a viscosity, measured at 25°C., of less than or equal to 1000 mPa.s.
 12. The composition accordingto claim 1, wherein the reactive diluent contains at least one hydroxy,aldehyde, epoxy, oxazolidine or lactone functional group.
 13. Thecomposition according to claim 12, wherein the reactive diluent ischosen from saturated or unsaturated alicyclic alcohols, saturated orunsaturated cyclic alcohols, mononuclear or polynuclear aromaticalcohols, glyoxal, glycidyl ethers of saturated or unsaturated alcohols,epoxidized fatty acids, oxazolidines and lactones.
 14. The compositionaccording to claim 1, wherein the reactive diluent is chosen fromfurfuryl alcohol, cardols and derivatives thereof (CNSL), glyoxal,1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether,epoxidized cardanols, bisoxazolidines and gamma-butyrolactone.
 15. Thecomposition according to claim 1, wherein the reactive diluentrepresents at least 10% by weight of the resin composition, and does notexceed 70%.
 16. The composition according to claim 1, wherein it alsoincorporates at least one crosslinking agent and/or one crosslinkingcatalyst.
 17. The composition according to claim 16, wherein thecrosslinking agent is chosen from compounds incorporating at least oneamine, hydroxy, aldehyde or carboxylic functional group, andheterocyclic compounds that have a structure incorporating a nitrogenatom and an oxygen atom separated by a carbon atom.
 18. The compositionaccording to claim 17, wherein the crosslinking agent is chosen fromaliphatic amines, polyamidoamines, aromatic amines,tris(hydroxymethyl)nitromethane, resins containing condensates obtainedby Mannich reaction of a phenolic compound, an aldehyde and an aminoalcohol, glyoxal and derivatives thereof, 2,2-dimethoxyethanal, acrylicacid homopolymers and copolymers, 1,3-phenylenebisoxazoline,3-ethyl-2-methyl-2-(3-methylbutyl)-1,3-oxazolidine and1-aza-3,7-dioxa(5-ethyl)bicyclo[3.3.0]octane.
 19. The compositionaccording to claim 16, wherein the crosslinking agent does not exceed50% of the weight of the liquid resin composition.
 20. The compositionaccording to claim 16, wherein the crosslinking catalyst is chosen fromthe Lewis bases selected from the group consisting ofO-(dimethylaminoethyl)phenol, tris(dimethylaminoethyl)phenol,2,4,6-tri(dimethylaminomethy)phenol, 2-methylimidazole,2-ethyl-4-methylimidazole and 1-benzyl-2-methylimidazole, and a Lewisacid selected from a boron trifluoride-monoethylamine complex.
 21. Thecomposition according to claim 16, wherein the amount of crosslinkingcatalyst in the liquid resin composition is less than or equal to 10parts by weight per 100 parts by weight of epoxy resin, reactive diluentand, optionally, crosslinking agent.
 22. An abrasive article comprisingabrasive grains connected by a binder based on a thermosetting resin,wherein the binder is the product of the crosslinking of the liquidresin composition according to claim
 1. 23. The article according toclaim 22, wherein the abrasive grains are grains made of alumina,including therein fused aluminas and sintered aluminas obtained by thesol-gel process, which may or may not be seeded by a material of thesame crystalline nature, and which may or may not be chemicallymodified, of iron oxide, molybdenum oxide, vanadium oxide,alumina-zirconia, boron-alumina, silicon carbide, aluminium oxynitride,diamond or cubic boron nitride, and mixtures of such grains.
 24. Thearticle according to claim 23, wherein the abrasive grains are treatedwith an organic compound that contains silicon, selected from the groupconsisting of silanes functionalized by organic groups.
 25. The articleaccording to claim 24, wherein the silane is a vinylsilane, anaminosilane, or an epoxysilane.
 26. The article according to claim 22,wherein it is a bonded abrasive.
 27. The article according to claim 22,wherein it is a coated abrasive.